Aqueous electronic circuit assembly cleaner and method

ABSTRACT

The present invention relates to environmentally safe aqueous cleaning compositions for cleaning electronic circuit assemblies, such as printed circuit or printed wiring boards, during their fabrication. Alkali metal carbonate and bicarbonate salts are utilized with an alkali metal silicate to achieve a variety of objectives, among which are the removal of solder flux, oils, waxes, and greasy substances, adhesives and other residues as well as provide anti-corrosion protection and metal brightening.

This application is a division of U.S. Ser. No. 896,660, filed Jun. 10,1992, now U.S. Pat. No. 5,234,506 which is a continuation-in-partapplication of U.S. Ser. No. 07/731,512, filed Jul. 17, 1991, nowabandoned.

FIELD OF THE INVENTION

The present invention relates to environmentally safe aqueous fluxremoving compositions for cleaning electronic circuit assemblies, suchas printed circuit or printed wiring boards, during their fabrication.Alkali metal carbonate and bicarbonate salts are utilized preferablywith various adjuvants, including a specified anti-corrosion andbrightening agent, to achieve a variety of objectives, among which arethe removal of solder flux, oils, waxes and greasy substances andadhesive and other residues.

BACKGROUND OF THE INVENTION

The cleanliness of electronic circuit assemblies (ECA), such as printedcircuit boards (PCB) or printed wiring boards (PWB), is generallyregarded as being critical to their functional reliability. Ionic andnonionic contamination on circuit assemblies is believed to contributeto premature failures of the circuit assemblies by allowing shortcircuits to develop.

In the manufacture of electronic circuit assemblies, ionic and nonioniccontamination can accumulate after one or more steps of the process.Circuit assembly materials are plated, etched, handled by operators inassembly, coated with corrosive or potentially corrosive fluxes andfinally soldered.

In the fabrication of electronic circuit assemblies, e.g., printedcircuit boards, soldering fluxes are first applied to the substrateboard material to ensure firm, uniform bonding of the solder. Thesesoldering fluxes fall into two broad categories: rosin and non-rosin, orwater soluble, fluxes. The rosin fluxes, which are generally onlymoderately corrosive and have a much longer history of use, are stillwidely used throughout the electronics industry. The water solublefluxes, which are a more recent development, are being used increasinglyin consumer products applications. Because water soluble fluxes containstrong acids and/or amine hydrohalides, such fluxes are very corrosive.Unfortunately, residues of any flux can cause circuit failure ifresidual traces of the material are not carefully removed followingsoldering and thus remain on an electronic circuit assembly.

While water soluble fluxes can be easily removed with warm, soapy water,the removal of rosin flux from printed circuit boards is more difficultand has therefore traditionally been carried out with the use ofchlorinated hydrocarbon solvents such as 1,1,1,-trichlorethane,trichloroethylene, trichloromonofluoromethane, methylene chloride,trichlorotrifluoroethane (CFC113), tetrachlorodifluoroethane (CFC112) ormixtures or azeotropes of these and/or other solvents. These solventsare undesirable, however, because they are toxic and when released intothe environment deplete the ozone layer and/or contribute to thegreenhouse global warming effect. Thus, use of such solvents is subjectto close scrutiny by the Occupational Safety and Health Administration(OSHA) and the Environmental Protection Agency (EPA), and stringentcontainment equipment must be used. Moreover, if released into theenvironment these solvents are not readily biodegradable and are thushazardous for long periods of time.

Alkaline cleaning compounds known as the alkanolamines, usually in theform of monoethanolamine, have been used for rosin flux removal as analternative to the toxic chlorinated hydrocarbon solvents. These high pHcompounds (e.g., about 12 pH), chemically react with rosin flux to forma rosin soap through the process of saponification. Other organicsubstances such as surfactants or alcohol derivatives may be added tothese alkaline cleaning compounds to facilitate the removal of suchrosin soap. Unfortunately, these compounds, as well as the water solublesoldering fluxes, have a tendency to cause corrosion on the surfaces andinterfaces of printed wiring boards if such compounds and fluxes are notcompletely and rapidly removed during the fabrication process.

In other approaches, Daley et al., U.S. Pat. No. 4,635,666 utilize ahighly caustic solution having a pH of 13 in a batch cleaning process.This method severely oxidizes the solder applied to the circuit board.In Hayes et al., U.S. Pat. Nos. 4,640,719 and 4,740,247 rosin solderingflux and other residues are removed from electronic assemblies by meansof terpene compounds in combination with terpene emulsifying surfactantsby rinsing in water.

The complete removal of adhesive and other residues also poses aproblem. During the manufacture of electronic circuit assemblies thecomponents are mounted on the upper surface of the board with leadsprotruding downwardly through holes in the board and are secured to thebottom surface of the board by means of an adhesive. Further, it issometimes necessary to temporarily protect certain portions of the boardfrom processing steps such as the process of creating corrosionresistant gold connecting tabs at the board edges. This transientprotection of portions of the circuit board can be achieved by theapplication of special adhesive tape to susceptible areas. Once suchprotection is no longer needed, the adhesive tape must be removed. Inboth instances, a residue of adhesive generally remains which, if notthoroughly removed, can cause premature board failure. Removal of thisadhesive residue has traditionally been carried out by the use ofchlorinated solvents which, as already described, are toxic andenvironmentally undesirable.

Thus, the residual contaminants which are likely to be found onelectronic circuit assemblies and which can be removed by thecompositions and method of the present invention include, but are notlimited to, for example, rosin flux, photoresist, solder masks,adhesives, machine oils, greases, silicones, lanolin, mold release,polyglycols and plasticizers.

In copending, commonly assigned U.S. Ser. No. 731,512, filed Jul. 17,1991, now abandoned, improved cleaning compositions characterized bynon-corrosiveness and low environmental impact, unlike the prior artchlorinated hydrocarbon solvents and alkaline cleaners, are employed forprinted wiring board and printed circuit board cleaning. As disclosedtherein, printed circuit/wiring board cleaning compositions are providedcomprising alkali metal carbonate and bicarbonate salts so combined thatthey have, when used in concentrations of about 1 to 15 percent byweight, a Ph of from about 10, or less, to 12 and an adequate reserve oftitratable alkalinity, at least equivalent to from about 0.2 to 4.5percent caustic potash (potassium hydroxide), when titrated to thecolorless phenolphthalein end point. At least about 50 percent and,preferably, at least about 65 percent by weight of the and bicarbonatecarbonate salts comprise potassium carbonate. The aqueous cleaningsolutions generally contain from about 1 to 15 percent or even moredepending on the particular conditions and, preferably, from about 2 to8 percent by weight of the salts comprising the cleaning composition. Inaddition, the cleaning solutions usually contain a small amount, e.g.,from about 50 to 5000 ppm of a water soluble reducing agent (oxygenscavenger). Preferably, the cleaning solutions also contain at use asmall amount, e.g., up to about 0.1 percent by weight of an antifoamagent. These, as well as other adjuvants, e.g., wetting agents,surfactants, etc., can be included with the salts per se or in anysolution thereof no matter what the concentration of salts therein. Whenused according to the above, the compositions do not leave anundesirable residual film.

While the cleaning compositions of the above-mentioned copendingapplication advantageously achieve the objectives stated therein such asproviding a method for the safe and effective removal of rosin solderingfluxes from electronic circuit assemblies such as printed circuit boardswithout otherwise adversely affecting the boards, further improvementwith respect to providing anti-corrosion protection to metal componentsincluding the solder joints as well as the connecting tabs along theedges of the boards and for providing brightening of all solder jointsand metal connectors is still needed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide compositions andmethods for the safe and effective removal of rosin soldering fluxesfrom electronic circuit assemblies, e.g., printed circuit boards,without otherwise adversely affecting the boards. It is a furtherobjective of this invention to provide safe and effective compositionsand methods for the removal of other residual contaminants from printedcircuit assemblies. Still further, another objective of the invention isto provide anti-corrosion protection to the printed circuit assembliesand to brighten solder joints, metalized connecting tabs at the boardedges and other metal or metalized features of the assemblies.

This invention provides cleaning compositions and methods for theremoval of rosin solder fluxes and other residues during the fabricationof printed circuit or wiring boards. As a result, the possibility ofpremature circuit failure that might occur in the absence of suchcleaning is eliminated or greatly reduced. The cleaning efficacy of thecompositions of the invention is such that printed wiring boards thustreated meet stringent U.S. Department of Defense specifications.

The compositions of the invention are characterized by non-corrosivenessand anti-corrosive protection as well as low environmental impact,unlike the chlorinated hydrocarbon solvents and highly alkaline cleanersthat have heretofore been employed for printed wiring board and printedcircuit board cleaning. Advantageously, the flux removing compositions,as used herein, exhibit lower biological oxygen demands (BOD) andchemical oxygen demands (COD) than formulations currently available. Forexample, BODs and CODs below 20,000 ppm in the wash water andconsiderably lower, e.g. less than 300 ppm in the rinse water resultupon using the cleaning compositions of this invention. Accordingly, therinse water can be sewered without further treatment and minimal, ifany, treatment is needed to remove the organics from the wash waterbefore sewering, thus eliminating the need for costly water treatment.

The present invention provides printed circuit/wiring board cleaningcompositions essentially formed from the aqueous cleaning compositionsas set forth in aforementioned U.S. Ser. No. 731,512now abandoned, andcomprising alkali metal carbonate salts or a mixture of alkali metalcarbonate and bicarbonate salts. At least about 50 percent and,preferably, at least about 65 percent by weight of the carbonate saltscomprise potassium carbonate. The aqueous cleaning solutions generallycontain from about 0.1 to about 15 percent by weight of the salts ormore depending on the particular conditions. In addition and inaccordance with the improvements found with respect to anti-corrosionprotection and metal brightening, the aqueous cleaning solutions of thisinvention further contain from about 0.01 to 2 percent by weight of analkali metal silicate. Other adjuvants, e.g., wetting agents, anti-foamagents, surfactants, etc., can be included with the salts per se or inany solution thereof no matter what the concentration of salts therein.

BRIEF DESCRIPTION OF THE FIGURES

The efficacy of this invention will be better understood by reference toFIGS. 1-7 herein wherein the test results of certain embodiments of thecleaning solutions of this invention are illustrated.

FIGS. 1, 2, 4, and 6 represent typical curves showing the cleaningefficiencies of various concentrations of cleaning solutions resultingfrom visual testing as described herein.

FIGS. 3, 5, and 7 represent typical curves showing the cleaningefficiencies of various concentrations of cleaning solutions resultingfrom equilibrium resistivity measurements as described herein.

DETAILED DESCRIPTION OF THE INVENTION

The objects and advantages mentioned above as well as other objects andadvantages may be achieved by the compositions and methods hereinafterdescribed.

Essentially, the flux removing compositions of this invention comprisecertain alkali metal salts and alkali metal salt mixtures asspecifically set forth in afore-mentioned U.S. Ser. No. 731,512, nowabandoned, with the addition of an alkali metal silicate. Accordingly,the term "flux removing compositions" as used herein is intended todefine the mixture of active ingredients comprised of the alkali metalsalts including the added alkali silicate and, if desired, any addedadjuvants as hereinlater described.

As hereinlater set forth, the flux removing compositions may beformulated into concentrated solutions. The terms "flux removingconcentrated solutions" or "concentrates" as used herein define aqueousmixtures containing from about 5 to 45 or more percent by weight of theflux removing compositions with the balance being essentially water.

As used herein the terms "flux removing solutions" or "flux removingsolutions in use" is meant to define aqueous mixtures containing fromabout 0.1 to 15 percent by weight of the flux removing composition withthe balance comprised essentially of water and which are the solutionsemployed in the cleaning methods of the invention. Also, as used herein,"flux removing composition" and "cleaning composition" have the samemeaning since as stated previously, the electronic circuit assembliesincluding printed circuit boards and printed wiring boards often containresidues other than fluxes which the compositions of this invention areable to remove and thus "flux removing composition" is intended as anall-purpose cleaner.

In accordance with the invention, additives, adjuvants, or the like, maybe included with the flux removing compositions, flux removingconcentrates, or the flux removing solutions in use.

The flux removing compositions of the present invention contain alkalimetal carbonates or mixtures of alkali metal carbonates andbicarbonates. The alkali metals contemplated include potassium, sodiumand lithium, with potassium being preferred. The carbonate salts includepotassium carbonate, potassium carbonate dihydrate, and potassiumcarbonate trihydrate, sodium carbonate, sodium carbonate decahydrate,sodium carbonate heptahydrate, sodium carbonate monohydrate, sodiumsesquicarbonate and the double salts and mixtures thereof. Thebicarbonate salts include potassium bicarbonate, sodium bicarbonate,lithium bicarbonate and mixtures thereof. Generally, the cleaningcompositions of the invention will contain the carbonate salts inamounts of from about 65 to 99 percent, preferably, about 82.5 to 92.5percent, for example, about 87.5 percent by weight. The and bicarbonatecarbonate salts comprise at least about 50 percent, preferably at leastabout 65 percent, for example, about 75 percent by weight of potassiumcarbonate. The bicarbonate salts are present in the cleaning compositionin amounts of about 0 to 25 percent, preferably, about 0 to 15 percent,for example, about 12.5 percent by weight. As set forth above, thealkali metal carbonate and bicarbonate salts are utilized incombinations and in concentrations such that the resultant solutionshave a pH of from about 10, or somewhat less, to 13, preferably fromabout 10 to less than 12 and, more preferably from 10.5-10.9. Thedesired pH of the cleaning solution may depend on the type of flux beingremoved. Thus, the lower pH range is desirable and effective forremoving the more easily removed fluxes. However, a pH of above 11.5 ispreferred when removing the more difficult to remove solder pastefluxes. It is most desirable that the salts used in combination at thedilution of the wash bath and at the desired pH also have an adequatereserve of titratable alkalinity, as least equivalent to from about 0.2to 4.5 percent caustic potash (potassium hydroxide), when titrated tothe colorless phenolphthalein end point, which is at about pH 8.4.

The cleaning compositions of the present invention also include analkali metal silicate which is added for the purpose of providingimproved anti-corrosion protection to the printed circuit board as wellas to brighten up all metallic surfaces including the solder joints aswell as any connecting tabs and the like. Thus, any of the lithium,sodium or potassium silicates are useful in the cleaning compositions ofthis invention. Preferably, however, the sodium and potassium salts areutilized and, most preferably, potassium silicate is used. The alkalimetal silicates which are used can be in a variety of forms which can beencompassed generally by the formula M₂ O:SiO₂ wherein M represents thealkali metal and in which the ratio of the two oxides can vary. Mostuseful alkali metal silicates will have an M₂ O to SiO₂ mole ratio ofbetween 1:0.5 and 1:4.5. Most preferably, the M₂ O to SiO₂ ratio isbetween 1:1.6 and 1:4.0. Such silicates also provide additionalalkalinity to the wash water to help cleaning. Surprisingly, it has alsobeen found that the addition of silicate actually promotes thebrightness and shininess of the solder joints.

The alkali metal silicate will be present in the cleaning composition inamounts ranging from about 0.1 to 10wt.% based on the active components.The alkali metal silicate, most preferably, potassium silicate can beadded to the dry salts and can also be added directly to the concentrateor to the wash bath. In each case, the alkali metal silicate will beused in an amount to comprise about 0.01 to 2wt. % of the cleaningsolution during use.

The cleaning compositions of the present invention which are comprisedof carbonate, bicarbonate and silicate salts as set forth above aregenerally prepared as aqueous concentrates. Such aqueous cleaningconcentrates may contain from about 5 up to about 45, or more, percentby weight of the salts depending on their solubility in water.Preferably, the concentrates contain about 10 to 40 percent, forexample, about 15 percent by weight of the cleaning composition (i.e.,carbonate, bicarbonate and silicate salts) with the remainderessentially water. The dilutions of these concentrates are determined bymanufacturing, packaging, shipping, storage, and other factors. Itshould be understood that the amount of solute in these concentrates isnot especially critical.

The flux removing solutions which are employed in the cleaningprocedures described herein usually contain from about 0.1 to 15, ormore, percent, preferably, from about 0.6 to 15 percent and, morepreferably, from about 1 to 3 percent by weight of the cleaningcompositions of this invention with the balance being essentially water.The upper limit of concentration of the cleaning composition is notcritical and is determined by fabrication conditions, the amount ofresidues and the difficulty of removing same from the circuitassemblies, etc.

Adjuvants, additives, and the like may be also employed in the cleaningcompositions, concentrates or the cleaning solutions as described andused herein. Thus, in accordance with the invention, at least onewater-soluble reducing agent and/or antioxidant may be employed. Thereducing agents include, alone or in combination, sodium bisulfite andhydrazine hydrate, which are the preferred reducing agents, theaminoboranes, e.g., dimethylamine borane, the alkali-metal borohydrides,e.g., potassium borohydride, the alkali-metal hydrophosphites andhydrosulfites, e.g., sodium hydrosulfite, and formalin. Other preferredreducing agents include dihydrazine sulfate and other salts thereof.

The reducing agent employed may also be an hydroxylamide, or anhydroxylamine addition salt, e.g., hydroxylamine sulfate, hydroxylaminehydrochloride, hydroxylamine nitrate, hydroxylamine acetate,hydroxylamine formate, hydroxylamine bromide, and the like, and mixturesthereof. Other salts such as potassium pyrosulfate, sodiumhypophosphite, sodium and potassium sulfite, sodium bisulfite, sodiummetabisulfite, sodium dithionite, sodium formaldehyde sulfoxylate, zincformaldehyde sulfoxylate, sodium nitrite, and mixtures thereof can alsobe used.

The water soluble reducing agent is supplied in an amount which issufficient to substantially, if not completely, preclude the oxidationof solder to its "dull" state and maintain it in its "shiny" state whichis deemed important to assess the adequacy of the soldered joints orconnections. In this aspect, the reducing agent acts as an adjunct tothe alkali metal silicate which is added as the primary "brightening"agent. The concentration of the reducing agent with the cleaningcomposition should be an effective amount which will generally rangefrom about 50 to 5000 ppm, preferably, about 100 to 1000 ppm, of thetotal aqueous cleaning solution in use. Amounts included in the cleaningcompositions and concentrates can be calculated accordingly.

The antioxidants which maybe employed in accordance with the inventioninclude butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT),terbutyl hydroquinone (TBHQ), the tocopherols, and the like. Generallythe antioxidants are employed in amounts such that the cleaning solutioncontains from about 10 to 1000 ppm and, preferably, from about 50 to 500ppm, of the aqueous cleaning solution in use.

It is also preferred to include at least one antifoam agent in any ofthe flux removing compositions of this invention. The antifoam agent isutilized to prevent the formation of excessive foam caused by the rosinflux/flux removing combination. The presence of foam interferes with themechanical action of the cleaning equipment used to wash the circuitboards. It is important, if not critical, that the antifoam agent usedherein does not act by replacing the flux film with another residualsurface film which could affect the performance of the electroniccircuit board in use. The antifoam agent could be an agent which solelyacts to inhibit foam or it could be a surfactant which helps clean theboards and emulsify soils.

Preferred examples of antifoam agents include compounds formed bycondensing ethylene oxide with a hydrophobic base formed by thecondensation of propylene oxide with propylene glycol. The hydrophobicportion of the molecule which exhibits water insolubility has amolecular weight of from about 1,500 to 1,800. The addition ofpolyoxyethylene radicals to this hydrophobic portion tends to increasethe water solubility of the molecule as a whole and the liquid characterof the product is retained up to the point where polyoxyethylene contentis about 50 percent of the total weight of the condensation product.Examples of such compositions are the "Pluronics" sold byBASF--Wyandotte. These compounds also enhance flux removal.

Other suitable antifoam agents that also enhance flux removal include:the polyethylene oxide/polypropylene oxide condensates of alkyl phenols,e.g., the condensation products of alkyl phenols having an alkyl groupcontaining from about 6 to 12 carbon atoms in either a straight chain orbranched chain configuration, with ethylene oxide/propylene oxide, theethylene oxide being present in amounts equal to 1 to 25 moles ofethylene oxide per mole of alkyl phenol and the propylene oxide beingpresent in amounts equal to 1 to 25 moles of propylene oxide per mole ofalkyl phenol. The alkyl substituent in such compounds may be derivedfrom polymerized propylene, diisobutylene, octene, or nonene, forexample.

Also suitable are those derived from the condensation of ethylene oxidewith the product resulting from the reaction of propylene oxide andethylene-diamine or from the product of the reaction of a fatty acidwith sugar, starch or cellulose. For example, compounds containing fromabout 40 percent to about 80 percent polyoxyethylene by weight andhaving a molecular weight of from about 5,000 to about 11,000 resultingfrom the reaction of ethylene oxide groups with a hydrophobic baseconstituted of the reaction product of ethylene diamine and excesspropylene oxide, and hydrophobic bases having a molecular weight of theorder of 2,500 to 3,000 are satisfactory.

In addition, the condensation product of aliphatic alcohols having from8 to 18 carbon atoms, in either straight chain or branched chainconfiguration, with ethylene oxide and propylene oxide, e.g., a coconutalcohol-ethylene oxide-propylene oxide condensate having from 1 to 30moles of ethylene oxide per mole of coconut alcohol, and 1 to 30 molesof propylene oxide per mole of coconut alcohol, the coconut alcoholfraction having from 10 to 14 carbon atoms, may also be employed.

The antifoam agents of the present invention are preferably employed inthe flux removing compositions at about 0.01 to about 10wt. % and in theflux removing solution in amounts of up to about 0.1 percent by weight,preferably, about 0.01 to 0.05 percent by weight based on the totalweight of the aqueous flux removing solution. The antifoam agents thus,can be included in the flux removing compositions, the concentrates andsolution so as to result in the desired concentrations during use.

The present invention also contemplates the use of one more surfactantsin the flux removing solutions in order to enhance the wetting andemulsifying ability of the flux remover and permit maximum penetrationthereof within regions of the circuit boards most difficult to clean.The surfactant used could be the same agent used to control the foam.Suitable surfactants include anionic, nonionic, cationic surfactants oramphoteric surfactants or combinations thereof. The surfactants shouldbe soluble, stable and, preferably, nonfoaming in use. A combination ofsurfactants may be employed. The term "surfactant", as used herein, mayinclude other forms of dispersing agents or aids.

It has been found especially effective to use alkoxylated alcohols whichare sold under the tradename of "Polytergent SL-Series" surfactants byOlin Corporation. Also, the polycarboxylated ethylene oxide condensatesof fatty alcohols manufactured by Olin under the tradename of"Polytergent CS-1" have also been found effective, especially incombination with the above Polytergent SL-Series surfactants. Aneffective surfactant which also provides antifoam properties is"Polytergent SLF-18" also manufactured by Olin. A combination of thissurfactant together with the above two surfactants has been found toprovide excellent cleaning with low foam.

Examples of other suitable surfactants are the block copolymers ofethylene oxide and propylene oxide such as those supplied by the BASFCorporation as Pluronics.

Ethoxylated alcohols with 8 to 20 carbons, such as those containing from3 to 30 moles of ethylene oxide per mole of alcohol could be used assurfactants in this invention. The monocarboxylated derivatives of thesesurfactants could also be used.

Sodium or potassium salts of sulfonated benzene or naphthalenederivatives such as alkyl benzene sulfonate, or alkyl naphthalenesulfonate or disulfonate could be used. However, caution would have tobe employed since these surfactants might tend to impart excessiveuncontrollable foam to the wash water.

The amounts of surfactant utilized is usually small, e.g., from lessthan 1% in the wash bath, but will vary depending on the conditions andthe contamination encountered and higher surfactant levels may beemployed if so desired.

The compositions of this invention are characterized by lowenvironmental impact, unlike the chlorinated hydrocarbon solvents andother materials that had been used prior to this invention for printedcircuit board cleaning. For example, the alkali metal carbonate andbicarbonate salts are naturally occurring and environmentally benign.The flux removing compositions of the invention have biological oxygendemand (BOD) and chemical oxygen demand (COD) values (as determined bymethods hereinafter described more fully) which are much lower thanalternative compositions currently available. As described in theExamples herein, the flux removing compositions result in very low BODsand CODs in the rinse water allowing the rinse water to be seweredwithout further treatment. In comparison, terpenes, e.g., limoneneresult in rinse water having BODs and CODs which may require removalbefore sewering.

The applicability of the compositions of the invention to variousaspects of the printed circuit/wiring board fabrication process can bestbe understood by a description of a representative assembly process.

The assembly manufacturing process involves the placement of componentssuch as integrated circuits, resistors, capacitors, diodes, etc. on thesurface of the board or their insertion through pre-drilled holes. Thecomponents are then secured by soldering by mechanical or automaticmeans. Interspersed with the soldering operations are cleaningprocedures and inspections to ensure that tape and solder flux residuesthan could lead to premature circuit failure do not remain.

For the removal of rosin soldering flux deposits and other residuesduring printed circuit/wiring board fabrication, the compositions of theinvention may be applied to the boards by immersion in dip tanks or byhand or mechanical brushing. Alternatively, they may be applied by anyof the commercially available printed wiring board cleaning equipment.Dishwasher size units may be employed, or much larger cleaning systemssuch as the "Poly-Clean+" and the various "Hydro-Station" modelsproduced by Hollis Automation, Inc. of Nashua, N.H.

Depending upon their design, these washers may apply the cleaningcompositions of the invention by spraying with mechanical nozzles or byrolling contact with wetted roller surfaces. The temperature at whichthe compositions may be applied can range from room, or ambient,temperature (about 70° F.) to about 180° F., preferably, about 140° to170° F. The cleaning compositions or concentrates are diluted with waterto as low as about 0.1 percent by weight (or volume) concentration.

Once solder flux has been loosened and removed during a period ofcontact which typically ranges from about 1 to about 5 minutes, but maybe longer, up to 10 minutes, the boards are taken from the flux removingsolution. Another advantage of the instant invention is that the fluxremoving solutions need not be flushed with solvents as with theprocesses of the prior art. Herein, the boards may simply be flushedwith water for a period of up to about 2 minutes. Deionized water ispreferred. The optimal rinsing time varies according to the kinds ofsurfactants and the concentrations of the flux removing solutions usedand can easily be determined by routine experimentation.

The cleaned boards are then dried, preferably with forced air. Drying isexpedited if the air is warmed, preferably to above about 100° F.

The efficacy of rosin soldering flux removal from printed wiring boardsis such that the boards meet stringent military specifications for lowresistivity after cleaning. For example, the boards meet theMil-P-28809A standard for low resistivity of the solvent extractsresulting when the contamination has been removed from a circuit boardcleaned according to Mil-P-55110C. The resistivity of such solventextracts after the cleaning of the boards is complete is most easilydetermined with an Omega Meter. Omega Meter is the registered trademarkof Kenco Industries, Inc., Atlanta, Ga., for a microprocessor-controlledcontamination test system that rapidly measures changes in resistivitydue to contaminating ions.

The results of Omega Meter measurements are expressed in equivalentunits of ug NaCl/in² or its metric equivalent. According toMIL-P-28809A, the acceptable resistivity value for a cleaned board isequivalent to 2.2. ug NaCl/cm² or 14 ug NaCl/in², but far better resultsare routinely obtained after solder flux has been removed with thecleaning solutions of the present invention. A value of about 0.31 ugNaCl/cm², or 2.0 ug NaCl/in², or even less, is typical.

The cleaning solutions of this invention are also effective in removingother undesirable and deleterious substances and residues. Oneparticularly troublesome substance is the residue left by adhesive tapeused during fabrication of the electronic circuit assemblies.

During the process of gold plating connecting tabs to improve corrosionresistance, tin-lead residues must first be removed from the unplatedtabs. Removal of these residues is carried out through the use ofetching chemicals that can damage other unprotected printedcircuit/wiring board components. To protect vulnerable components fromthe etching chemicals, boards are wrapped on both sides with an adhesiveplating tape which forms a shield or splash guard for all but theexposed tab area. The etching chemicals then remove the tin-leadresidues on the tabs, a nickel plate is applied as a base for the gold,and gold plating of the tabs is finally carried out. The adhesiveplating tape which is maintained in place through all of these etchingand plating steps, is then removed. When the tape is removed followingthe nickel and gold plate step, it is at this point that the cleaningcompositions of the invention may most advantageously be used.

Thus, following removal of the tape, a silicone-based and/orrubber-based adhesive residue may remain on the board. This residue mayeasily be removed by employing the compositions of the invention underthe same conditions described above for solder flux removal. The exactoperational parameters will be determined by the nature of the adhesiveresidue and the tenacity with which it adheres to the board, but theconditions described above are generally effective. As in the case ofsolder flux removal, treatment of the board with the cleaning solutionsof the invention is generally followed by water flushing and air drying.

The efficiency of removal of adhesive residues from printedcircuit/wiring boards by the compositions of the invention is such thatno residues are visible after cleaning. A simple 5-10X stereomicroscopecan facilitate visual inspection for tape residues following cleaning.

The following non-limiting Examples are provided to further illustratethe present invention. All percentages, unless otherwise noted, are byweight. However, due to the near equivalence of the weight and volume ofthe materials utilized, volume percent is essentially the same.

EXAMPLES I-IV

To illustrate the cleaning ability of the cleaning compositions of theinvention, a series of demonstration printed wiring boards were cleanedin a mechanical cleaning system.

The cleaning composition contained, by weight, 75 percent potassiumcarbonate, 12.5 percent sodium bicarbonate, and 12.5 percent sodiumcarbonate monohydrate. Cleaning solutions having various concentrationswere prepared.

The cleaning system was a "Poly-Clean+" machine which is manufactured byHollis Automation, Inc. of Nashua, N.H.

The cleaning sequence comprised the operations of loading, washing,drying, first rinsing, final rinsing and high speed drying carried outin succession. The washing operation utilizing cleaning solutions of theinvention was done in two stages, i.e., a first regular wash at spraynozzle manifold which directed a regular wash spray at 40 psig followedby a "hurricane" spray at 80 psig. The cleaning solutions weremaintained at 160° F. The rinses were also two stage operations; thefirst at 40 psig regular rinse followed by an 80 psig "hurricane" rinsewith the rinse water having a temperature of 160° F. A final rinse waseffected under substantially the same conditions. The circuit boardswere subjected to Alpha air knife drying after the washing and finalrinse stages. In air knife drying, turbine propelled air shears fluidsfrom the boards' surfaces.

Cleaned and dried boards were evaluated for cleaning efficiency bothvisually and by an Alpha 600 5MD Omega Meter resistivity measurements.

The visual test method uses a dyed flux and carrier base injectedbetween glass components and a glass board. This provides excellentaccess for visual inspection. The analysis is further quantified byplacing the board and components against a grid. Each block of the gridis then read as being completely clean or containing residue.

The test method utilizes straight flux and carrier from a rosin mildlyactivated (RMA) flux or paste. It is essentially the solder paste minusthe solder. "Carrier" refers to both the flux paste and all otheradditives included in solder paste, except the solder. This carrier isthen injected with red dye so that visual examination can be made morerapidly. The dye does not affect the carrier density or meltingproperties. The dyed carrier is then injected under the glass componentson specially made test boards. RMA solder paste is not considered anaqueous-compatible flux. The test boards are constructed of glass. A1"×1" square coupon that simulates the component is mounted onto a glasssubstrate. The coupon is glued in place by first laying shim stock ofthe desired standoff height on the glass. Next, the glue is applied andthe coupon set in place until it dries. When dry, the shim stock isremoved. Six coupons are mounted on a single board at 1/2" spacing. Theinterior coupons are further shielded from any nozzles by the firstcoupons in the placement array.

The flux carrier stock is injected under each coupon to entirely fillthe inch-square area. Flux is also added to the area surrounding eachcoupon. The board is IR-reflowed at a typical dwell time of five minutesat reflow temperature. All boards are then stored for 24 hours atambient temperature prior to cleaning. Reflowing and storing increasescleaning difficulty by allowing the board to cool and the flux carrierto set up.

Prior to reflow, the entire area under the coupon is filled with thedyed flux carrier. During reflow, a small percentage of the area underthe coupon develops voids due to expansion and escape of flux volatiles.The area under the coupons filled with baked-on residue is measuredprior to cleaning. The application method causes most of the flux to bebridged across the component standoff height. These regions entirelyfilled with flux are the most difficult to clean. They are also muchless likely to occur in actual manufacturing processes since much lessflux is applied. For the purposes of this test, however, no specialmeasurement qualification is given to this category. By regarding allareas with flux trapped under them as the same, the test method is mademore rigorous. This method is directed toward the measurement ofcleaning effectiveness, which is defined as the percentage of residueremoved. This aqueous cleaning test method is described more fully in apublication by Janet R. Sterritt, "Aqueous Cleaning Power," PrintedCircuit Assembly, September 1989, pp. 26-29.

The results from the cleaning experiments are measured in terms ofcleaning effectiveness as follows. The area of reflowed flux carrier ismeasured prior to cleaning. The test board is then cleaned and theamount of flux residue is visually measured with the aid of a gridpattern. The cleaning effectiveness rating is established by dividingthe area still containing flux after cleaning by the total areacontaining flux prior to cleaning. The measurement technique shows thata completely clean board would result in a cleaning effectiveness ratingof 100%. A test board on which three quarters of the initial residue isremoved would show a 75% reading.

To make the resistivity measurements, cleaned and dried boards wereloaded into a test cell of the instrument and then extracted with acirculating solution of isopropanol: water (25:75), v/v) as specified byMIL-P-55110C and MIL-P-28809A. The resistivity of the solution wasmeasured at a rate of 24 times per minute over a period of about 5-15minutes until equilibrium was reached, indicating that extraction ofboard surface contamination was essentially complete. Equilibrium wasdefined as the point at which the change in measured resistivity of thesolution was less than or equal to 5% of any value measured in theprevious two minutes.

EXAMPLE I

In this example, demonstration glass printed wiring boards (as developedby Hollis Automation to evaluate cleaning solution and as hereinbeforedescribed more fully) which were reflowed with Alpha flux paste asdisclosed above were subjected to the sequence of cleaning operationsalso disclosed above. Five different concentrations of cleaningsolutions, i.e., concentrations of 1.0, 1.7, 2.6, 3.5 and 6.0 percentwere employed. Three different standoff distances were employed, viz., 2mils, 6 mils, and 10 mils, respectively.

The results are shown in FIG. 1 in terms of cleaning effectiveness.These results clearly demonstrate the efficacy of the cleaning solutionsof the present invention, especially at concentrations of 2.0 percentand above. The efficacy of the cleaning solutions at standoffs as low as2 mils is especially noteworthy because of the difficulty in accessingthe flux.

EXAMPLE II

Demonstration (H-40) circuit boards (circuit boards produced by HollisAutomation and which ware provided with drilled holes for the passage ofleads therethrough) were immersed in flux and wave soldered with Kester185 and evaluated both visually and on the Alpha 600 5MD Omega Meter forionic contamination. FIGS. 2 and 3 illustrate the results of suchevaluations. The visual evaluation in FIG. 2 again illustrates theeffectiveness of the cleaning solutions of this invention. FIG. 3confirms the visual results by extremely low ionic contaminationresults. FIG. 3 shows a concentration of about 2 percent results in anacceptable resistivity value of about 14 ug NaCl/in² according toMIL-P-28809A. The equilibrium resistivity measurements for the cleaningtests of Example II are also shown in Table I.

                  TABLE I                                                         ______________________________________                                        RESISTIVITY MEASUREMENTS OF CLEANED ROSIN                                     FLUX SOLDERED PRINTED WIRING BOARDS                                                      Cleaner     Equivalent NaCl                                        Test       Concentration                                                                             Contamination                                          Number     (weight %)  (ug/in.sup.2)                                          ______________________________________                                        1          1.0         29.6                                                   2          1.7         16.0                                                   3          2.6         12.0                                                   4          3.5          4.0                                                   5          6.0          1.6                                                   ______________________________________                                    

As shown in Table 1, the cleaning solutions examined were effective atconcentrations below 2.0 percent in producing levels of residual boardsurface contamination that were far below the MIL-P-28809A requirementof 14 ug NaCl/in² equivalent. This is especially noteworthy in view ofthe configuration of the boards subjected to testing.

EXAMPLE III

Demonstration (H-50) circuit boards (produced by Hollis Automation andhaving fewer joints, etc. as the H-40 boards) were wave soldered withKester 185.

Both FIGS. 4 and 5 support the surprising effectiveness of the cleaningsolutions of the present invention by both visual testing (FIG. 4) andby Omega Meter testing for ionic contamination (FIG. 5).

Table II also shows the equilibrium resistivity measurements for thecleaning tests of Example III.

                  TABLE II                                                        ______________________________________                                        RESISTIVITY MEASUREMENTS OF CLEANED ROSIN                                     FLUX SOLDERED PRINTED WIRING BOARDS                                                      Cleaner     Equivalent NaCl                                        Test       Concentration                                                                             Contamination                                          Number     (weight %)  (ug/in.sup.2)                                          ______________________________________                                        1          1.7         5.0                                                    2          2.6         3.6                                                    3          3.5         2.4                                                    4          6.0         0.8                                                    ______________________________________                                    

As shown in Table II, the cleaning concentrations examined were alleffective in producing levels of residual board surface contaminationthat were far below the MIL-P-28809A requirement of 14 ug NaCl/in²equivalent.

EXAMPLE IV

In this example, demonstration circuit boards similar to those ofExample III were evaluated again both visually and for ioniccontamination on the Omega Meter. These demo boards were reflowed withKester R-229RMA paste. The results are shown in FIG. 6 which representsthe results from visual testing and FIG. 7 which represents the ioniccontamination results.

The equilibrium resistivity measurements for the cleaning tests effectedin Example IV are also shown in Table III.

                  TABLE III                                                       ______________________________________                                        RESISTIVITY MEASUREMENTS OF CLEANED ROSIN                                     FLUX SOLDERED PRINTED WIRING BOARDS                                                      Cleaner     Equivalent NaCl                                        Test       Concentration                                                                             Contamination                                          Number     (weight %)  (ug/in.sup.2)                                          ______________________________________                                        1          1.7         3.0                                                    2          2.6         0                                                      3          3.5         0                                                      4          6.0         0                                                      ______________________________________                                    

As shown in Table III, again, all the cleaning concentrations examinedwere effective in producing levels of residual board surfacecontamination that were far below the MIL-P-28809A requirement of 1.4 ugNaCl/in².

EXAMPLE V

For this Example separate tests were performed for effluent chemistryand aluminum abrasion in order to exemplify the environmental efficacyof the cleanings of this invention. The effluent tests measured pH, BODand COD. The methods employed are described in the following: (a) forchemical oxygen demand analysis see "Method for the Chemical Analysis ofWater & Wastes, USEPA 600/4 79 020, Method 410.1 and (b) for biologicaloxygen demand analysis see "Method for the Chemical Analysis of Water &Wastes, USEPA 600/4 79 020, Method 405.1.

Two samples were drawn from the wash tank utilized in the previousExamples I-IV. Sample No. 1 was at a concentration of 2.6 percent byweight and Sample No. 2 was at a concentration of 3.5 percent by weight.No additional dilution was made, e.g., by mixing with the rinse waterutilized. Each Sample was also measured for its pH. The results of thesetests and measurements are presented in Table IV.

                  TABLE IV                                                        ______________________________________                                                          Sample Number                                                                 1    2                                                      ______________________________________                                        Concentration (wt %)                                                                              2.6    3.5                                                BOD (ppm)           35     33                                                 COD (ppm)           71     71                                                 pH                  10.51  10.56                                              ______________________________________                                    

The results from the aluminum abrasion test showed no discoloration onthe heat sinks. The evidences no corrosion or other chemical attack ofaluminum surfaces.

The foregoing data clearly indicate the surprisingly low environmentalimpact accruing from the use of the cleanings of this invention. Theabove BOD and COD values are markedly and, advantageously, lower thanthose required by various federal and/or state environmental agencies.These desirably lower values are also valuable in that costlycontainment equipment and the accompanying processing steps are eithersubstantially reduced or rendered unnecessary.

EXAMPLE VI

This Example describes the methods utilized to attain the biologicaloxygen demand (BOD) and chemical oxygen demand (COD) values ofrepresentative concentrated cleaning solutions of this invention forcomparative purposes with those of the prior art.

Accordingly, samples of a 26 percent concentrated cleaning solution ofthis invention containing, by weight, 75 percent potassium carbonate,12.5 percent sodium bicarbonate and 12.5 percent sodium carbonatemonohydrate and the remainder, i.e., 74 percent, water were prepared andtested according to the USEPA tests 600/4 79 020, methods 410.1 and405.1 utilized in Example V.

The tests resulted in a BOD of less than 12 and a COD of less than 50.These value were reported as such since they were at the lowestthreshold values reproduced by the tests.

These values compare favorably with prior art saponifiers, see forexample, Hayes et al, U.S. Pat. Nos. 4,640,719 and 4,740,247 whereinBODs of about 295 and CODs of about 1,425 are reported.

EXAMPLE VII

This Example reports the pH values obtained from various concentratedcleaning solutions of the present invention.

In each test procedure the active ingredients were initially dry mixedand then 35 percent by weight thereof was added to 65 percent by weightof deionized water.

The pH of three different concentrated cleaning solutions were asfollows:

    ______________________________________                                        Cleaner                    pH                                                 ______________________________________                                        1.       75 wt % potassium carbonate                                                                         11.15                                                 12.5 wt % sodium bicarbonate                                                  12.5 wt % sodium carbonate monohydrate                                 2.       70 wt % potassium carbonate                                                                         10.80                                                   30 wt % sodium bicarbonate                                           3.       95 wt % potassium carbonate                                                                         11.97                                                   5 wt % sodium bicarbonate                                            ______________________________________                                    

Each of these cleaning concentrates exhibits a pH which isadvantageously compatible with the electronic circuit boards beingcleaned as well as the cleaning equipment presently utilized. Suchsolutions also are not environmentally detrimental and are easilyprocessable and/or recoverable.

EXAMPLE VIII

The procedures of each of Examples I-IV are repeated except that 500 ppmof sodium bisulfite is added to the cleaning solutions as a reducingagent. The demo boards are cleaned consistent with the procedures of theExamples and then are examined as before. Visual testing and Omega Metertesting results are each comparable to the results of the previoustests. Visual examination indicates that the soldered joints remainshiny and are not dulled due to oxidation.

EXAMPLE IX

The procedure of Examples I-IV and VIII are repeated except that 500 ppmof hydrazine hydrate is added to the cleaning solutions as a reducingagent. After cleaning, the demo boards are examined as before. Visualand Omega Meter testing results are comparable to those of the previoustests. Visual examination also indicates that the soldered joints remainshiny. A further benefit accrues in that the hydrazine hydratecompletely dissociates into water and leaves no film or residue.

EXAMPLE X

The procedures of each of Examples I-IV and VIII and IX are repeatedexcept that 0.05 percent by weight of Pluronic L101 is added to cleaningsolutions as an antifoam agent. Pluronic L101 is a poly(oxyethylene)poly(oxypropylene)-poly(oxyethylene) block copolymer having a molecularweight of about 3800 and is sold by BASF--Wyandotte. It is noted thatany foam resulting from the removal and agitation of the fluxes andother foam producing residues is reduced. Visual and Omega Meter testingresults are comparable to those of the previous tests.

EXAMPLES XI and XII

In the following two examples, the cleaning solutions were evaluated forcleaning and brightening efficacy on actual circuit boards using aHollis Hydro--station 332 machine. Throughput time was 1.5 minutes andthe bath temperature was 165° C.

    ______________________________________                                                           Examples                                                                      XI    XII                                                                     wt. % present                                                                 in wash bath                                               ______________________________________                                        Potassium carbonate  1.320   1.320                                            Sodium carbonate monohydrate                                                                       0.220   0.220                                            Sodium bicarbonate   0.220   0.220                                            Sodium polyacrylate  0.330   0.330                                            Sodium carboxymethylcellulose                                                                      0.150   0.150                                            Potassium silicate   0.036   0.109                                            (29% aqueous solution)                                                        Monotrope 1250       0.340   0.340                                            Pluronic 25R2        0.020   0.020                                            Plurafac RA30        0.020   0.020                                            ______________________________________                                         Monotrope 1250 is a tradename of Mona Industries and consists of a            solution of sodium nonanoate.                                                 Pluronic 25R2 is a tradename of BASF Wyandotte and consists of a block        copolymer of ethylene oxide and propylene oxide.                              Plurafac RA30 is a tradename of BASF Wyandotte and consists of an             alkoxylated surfactant alcohol.                                          

                  TABLE V                                                         ______________________________________                                        Visual Cleaning and Brightening Results                                       Flux type Board Type       XI      XII                                        ______________________________________                                                             Cleaning                                                 Alpha     H-40 Through hole                                                                              B        B-                                        Kester    H-40 Through hole                                                                               B-      B-                                        Alpha     Demo Surface mount                                                                             A       A                                          Kester    Demo Surface mount                                                                             A       A                                          ______________________________________                                         A = Completely Clean                                                          E = Not Clean                                                            

    Brightening                                                                   Alpha     H-40 Through hole                                                                              C       A                                          Kester    H-40 Through hole                                                                              C       A                                          ______________________________________                                         A = Very bright joints                                                        D = Very dull joints                                                     

The results show that both products were effective in removing thecommercial fluxes from circuit boards. However, it can be seen thatincreasing the silicate level dramatically increased the brightening ofthe joints.

EXAMPLES XIII, XIV and XV

In the following examples, cleaning compositions were prepared andevaluated for cleaning ability using a laboratory screening test. Forthe test, loops of copper wire are dipped into molten rosin flux solderpastes and care is taken to ensure that a thick film of flux remains onthe "joint" so formed. The rosin fluxes used represent the moredifficult to remove fluxes available.

The joints were washed for 5 minutes in a relatively gently stirredtemperature controlled 10% aqueous solution of the formulation beingevaluated. Removal of the flux was determined by visual examination.Results are shown in Table VI.

    ______________________________________                                                        Examples                                                                      wt. % present in formulation                                                  XIII   XIV      XV                                            ______________________________________                                        Potassium carbonate                                                                             12.60    13.20    13.20                                     Sodium carbonate monohydrate                                                                    5.30     5.50     5.30                                      Potassium hydroxide                                                                             0.00     0.00     1.20                                      (50% aqueous solution)                                                        Sodium hydroxide  0.90     0.90     0.00                                      (50% aqueous solution)                                                        Polyacrylic acid  5.00     5.00     5.00                                      (50% aqueous solution)                                                        Sodium carboxymethylcellulose                                                                   1.50     1.50     1.50                                      Potassium silicate                                                                              1.25     1.25     1.25                                      (29% aqueous solution)                                                        Monotrope 1250    3.40     3.00     4.40                                      Pluronic 25R2     0.19     0.00     0.00                                      Plurafac RA30     0.22     0.00     0.00                                      Polytergent CS-1  0.00     0.25     0.10                                      Polytergent SL-62 0.00     0.20     0.35                                      Polytergent SLF-18                                                                              0.00     0.05     0.05                                      Water             69.64    69.15    67.65                                     Total             100.00   100.00   100.00                                    Approximate pH    10.80    10.80    10.80                                     ______________________________________                                         Polytergent is a tradename of Olin Corp.                                      CS-1 is a carboxylated, ethoxylated fatty alcohol mixture, SL62 and SLF18     are alchoxylated fatty alcohol mixtures.                                 

                  TABLE VI                                                        ______________________________________                                        Visual cleaning results                                                                        Cleaning                                                              Wash      Rosin Flux Rosin Flux                                               temperature                                                                             A          B                                               ______________________________________                                        Example XIII                                                                             165° F.                                                                            4          3                                           Example XIV                                                                              145° F.                                                                            4          5                                           Example XV 165° F.                                                                            5          5                                           Control A  165° F.                                                                            5          3                                           Control B  165° F.                                                                            5          4                                           ______________________________________                                         1 = Very little removal                                                       3 = moderate removal                                                          5 = complete removal                                                     

Controls A and B, had as is pHs of 13.5 and 13.0, respectively, and werecommercially available aqueous flux saponifiers containingmonoethanolamine and 2-butoxyethanol as active ingredients. Each wasused at their recommended usage concentrations of 5% and 8%respectively.

The results show that all three example formulations were moderately tohighly effective in removing the rosin fluxes. They were comparable inperformance to the commercial products Controls A and B.

EXAMPLE XVI

The following samples were prepared and evaluated for their tendency tocorrode various aluminum substrates.

    ______________________________________                                                        wt. % present in formulation                                                  Examples                                                                             Controls                                                               XVI    C        D                                             ______________________________________                                        Potassium carbonate                                                                             15.84    0.00     13.20                                     Sodium carbonate anhydrous                                                                      0.00     10.60    0.00                                      Sodium carbonate monohydrate                                                                    0.56     2.18     2.18                                      Sodium bicarbonate                                                                              0.00     2.18     2.18                                      Sodium hydroxide (50%)                                                                          1.23     0.00     0.00                                      Polyacrylic acid (50% solution)                                                                 6.00     0.00     0.00                                      Sodium carboxymethylcellulose                                                                   1.50     0.00     0.00                                      Benzothiazolethiol                                                                              0.00     1.00     0.00                                      Potassium silicate                                                                              1.25     0.00     0.00                                      (29%, SiO.sub.2 :K.sub.2 O = 2.4)                                             Monotrope 1250    3.40     0.00     0.00                                      Pluronic 25R2     0.21     0.21     0.00                                      Plurafac RA30     0.23     0.23     0.00                                      Water             69.78    83.60    82.54                                     Total             100.00   100.00   100.00                                    Approximate pH    10.80    10.80    10.50                                     ______________________________________                                    

Corrosion Test

Squares of aluminum test coupons measuring approximately 3/4" squarewere accurately weighed. They were then immersed in 10% aqueoussolutions of the above formulations at 165° F. for 15 minutes. Thecoupons were rinsed in distilled water, air dried and reweighed. Loss ofweight is an indication of corrosion. The results are summarized below.

    ______________________________________                                                       % Loss in weight                                                              Example Controls                                               Aluminum Type    XVI       C        D                                         ______________________________________                                        Aluminum 1100    -0.01     -1.51    -2.22                                     Aluminum alloy 5052                                                                            0.02      0.67     0.93                                      Anodized aluminum 6061                                                                         0.00      -1.36    -1.97                                     ______________________________________                                    

It can be seen that the Example XVI containing potassium silicate waseffective in inhibiting corrosion of the aluminum coupons. In contrast,control D, containing no corrosion inhibitor and Control C, containingbenzothiazole, were highly corrosive to the aluminum substrates.

EXAMPLES XVII, XVIII AND XIX

The following electronic circuit board cleaners are useful alternativesto the strictly carbonate and/or bicarbonate cleaners of the previousexamples. The formulations set forth below are as effective for removingrosin flux and other residues as the wholly carbonate-based cleaners.

    ______________________________________                                                         Examples                                                                      XVII   XVIII    XIX                                          ______________________________________                                        Potassium pyrophosphate                                                                          12.00    0.00     4.00                                     Potassium tripolyphosphate                                                                       0.00     8.00     0.00                                     Trisodium phosphate                                                                              2.00     0.00     4.00                                     Potassium carbonate                                                                              0.00     0.00     8.00                                     Sodium metasilicate                                                                              5.00     8.00     2.00                                     Sodium silicate (3.1:1                                                                           2.00     4.00     0.00                                     ratio SiO.sub.2 :Na.sub.2 O)                                                  Potassium silicate (3.9:1                                                                        0.00     0.00     2.00                                     ratio SiO.sub.2 :K.sub.2 O                                                    Pluronic 17R4      0.00     0.20     0.20                                     Plurafac A-38      0.00     0.40     0.00                                     Nedol 25-7         0.00     0.00     0.20                                     Polytergent CS-1   0.40     0.00     0.10                                     Polytergent SLF-18 0.10     0.00     0.10                                     Sodium Carboxymethylcellulose                                                                    1.50     1.20     1.50                                     Sodium Octanoate   1.00     1.00     1.20                                     Water              qs       qs       qs                                       ______________________________________                                         Neodol 257 is an alcohol having a carbon chain length of C.sub.12-15 and      ethoxylated with an average of 7 mols. of ethylene oxide, Shell Chemical      Co.                                                                      

EXAMPLE XX

This example illustrates the improvement in brightening achieved byaddition of a silicate corrosion inhibitor to the alkaline salts.

    ______________________________________                                                           wt. % present                                                                 in wash bath                                                                    Control  Example                                                              E        XX                                              ______________________________________                                        Potassium carbonate  1.260    1.260                                           Sodium carbonate monohydrate                                                                       0.210    0.210                                           Sodium bicarbonate   0.210    0.210                                           Potassium silicate (44.1%                                                                          0.000    0.120                                           aqueous solution - D type)                                                    Pluronic 25R2        0.020    0.020                                           Plurafac RA30        0.020    0.020                                           ______________________________________                                         D Type silicate is supplied by PQ Corp. and has an SiO.sub.2 :K.sub.2 O       ratio of 2:1.                                                            

    Cleaning and Brightening on                                                   H-40 through hole boards                                                                     Cleaning Brightening                                           ______________________________________                                        Control E      B        C                                                     Example XX     A        A                                                     ______________________________________                                        A = Very clean    A = Very bright joints                                      E = Not clean     D = Very dull joints                                        ______________________________________                                    

Many modifications and variations of this invention maybe made withoutdeparting from its spirit and scope, as will become apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is limited only by theterms of the appended claims.

What is claimed is:
 1. A cleaning composition comprising (a)alkali-metal carbonate, or mixtures of alkali metal carbonate andbicarbonate salts, (b) an alkali metal silicate, (c) an antifoam agent,a surfactant or both and (d) sodium octanoate or sodium nonanoate,wherein (a), (b), (c) and (d) are so combined that when in an aqueouscleaning solution at a concentration of from about 0.6 to 15 percent byweight said solution has a pH of from about 10 to
 13. 2. The compositionof claim 1 wherein said (a), b), (c) and (d) are so combined at saidconcentration and pH to provide a reserve of titratable alkalinity atleast equivalent to from about 0.2 to 4.5% caustic potash when titratedto the colorless phenolphalein end point of about pH 8.4.
 3. Thecomposition of claim 1 which comprises from about 65 to 99 percent byweight alkali metal carbonate salts, from 0 to 25 percent by weightalkali metal bicarbonate salts, 0.1 to 10 percent by weight alkali metalsilicate, and the balance comprising said (c) and (d), characterized byat least 50 percent by weight of the alkali metal carbonate andbicarbonate salts comprise potassium carbonate.
 4. The composition ofclaim 1 wherein said alkali metal silicate is selected from the groupconsisting of sodium silicate, potassium silicate and mixtures thereofcharacterized by M₂ O to SiO₂ mole ratios of between 1:1.6 to 1:4.5,wherein M is sodium or potassium.
 5. The composition of claim 4 whereinsaid alkali metal silicate is potassium silicate.
 6. An aqueousconcentrated solution comprising from about 5 to 45 percent by weight ofa cleaning composition, said cleaning composition comprising (a)alkali-metal carbonate, or mixtures of alkali metal carbonate andbicarbonate salts, (b) an alkali metal silicate, (c) an antifoam agent,a surfactant or both and (d) sodium octonoate or sodium nonanoate,wherein (a), (b) (c) and (d) are so combined that when in an aqueouscleaning solution at a concentration of from about 0.6 to 15 percent byweight said solution has a pH of from about 10 to
 13. 7. The concentrateof claim 6 wherein said (a), (b), (c) and (d) are so combined at saidconcentration and pH to provide a reserve of titratable alkalinity atleast equivalent to from about 0.2 to 4.5% caustic potash when titratedto the colorless phenolphalein end point of about pH 8.4.
 8. Theconcentrate of claim 6 wherein said composition comprises from about 65to 99 percent by weight alkali metal carbonate salts, from 0 to 25percent by weight alkali metal bicarbonate salts, 0.1 to 10 percent byweight alkali metal silicate, and the balance comprises said (c) and(d), characterized by at least 50 percent by weight of the alkali metalcarbonate and bicarbonate salts comprise potassium carbonate.
 9. Theconcentrate of claim 6 wherein said alkali metal silicate is selectedfrom the group consisting of sodium silicate, potassium silicate andmixtures thereof characterized by M₂ O to SiO₂ mole ratios of between1:1.6 to 1:4.5, wherein M is sodium or potassium.
 10. The composition ofclaim 9 wherein said alkali metal silicate is potassium silicate.
 11. Anaqueous cleaning solution comprising from about 0.6 to 15 percent byweight of a cleaning composition, said cleaning composition comprising(a) alkali-metal carbonate, or mixtures of alkali metal carbonate andbicarbonate salts, (b) an alkali metal silicate, (c) antifoam agent,surfactant or both, and (d) sodium octonoate or sodium nonanoate,wherein, (a) (b), (c) and (d) are so combined that said solution has apH of from about 10 to
 13. 12. The solution of claim 11 wherein said(a), (b), (c) and (d) are so combined at said concentration and pH toprovide a reserve of titratable alkalinity at least equivalent to fromabout 0.2 to 4.5% caustic potash when titrated to the colorlessphenolphalein end point of about pH 8.4.
 13. The solution of claim 11wherein said composition comprises from about 65 to 99 percent by weightalkali metal carbonate salts, from 0 to 25 percent by weight alkalimetal bicarbonate salts, 0.1 to 10 percent by weight alkali metalsilicate, and the balance comprises said (c) and (d) characterized by atleast 50 percent by weight of the alkali metal carbonate and bicarbonatesalts comprise potassium carbonate.
 14. The solution of claim 11comprising from about 1 to 3 percent by weight of said cleaningcomposition.
 15. The solution of claim 11 wherein said alkali metalsilicate is selected from the group consisting of sodium silicate,potassium silicate and mixtures thereof characterized by M₂ O to SiO₂mole ratios of between 1:1.6 to 1:4.5, wherein M is sodium or potassium.16. The solution of claim 15 wherein said alkali metal silicate ispotassium silicate.